Method for processing biological fluid and treating separated component

ABSTRACT

Methods and systems for processing a biological fluid and treating a separated component of the biological fluid are disclosed.

TECHNICAL FIELD

This invention relates to methods, systems, and devices for processing abiological fluid, preferably including processing a separated componentof the biological fluid. More particularly, the present inventionconcerns obtaining blood from a source such as a donor, separating acomponent from the blood, treating the separated component, andreturning the component depleted blood to the source.

BACKGROUND OF THE INVENTION

An adult human contains about 5 liters of blood, which includes valuablecomponents such as red blood cells, liquid blood plasma and platelets.In view of the substantial therapeutic and monetary value of these bloodcomponents, a variety of techniques have been developed to separateblood into its component fractions while ensuring maximum purity andrecovery of each of the components. Additionally, since blood and bloodcomponents may include varying numbers of white blood cells(leukocytes), which may cause undesirable effects when administered to apatient, blood processing techniques may also include leukocytedepleting the blood or blood components, e.g., by passing the blood orblood components through a leukocyte depletion device.

In some techniques for blood processing, a container such as a flexiblebag is connected to a blood donor, and filled with a unit of wholeblood. The container is disconnected from the donor, and the blood isfurther processed to provide the desired separated component(s).Alternatively, in some other techniques, e.g., apheresis, the donor mayremain connected to a blood processing system during componentseparation, while the remainder of the blood, depleted of the desiredcomponent, is returned to the donor. Blood may be passed transverselyacross a membrane, e.g., a planar sheet or a bundle of hollow fibers, toseparate the component from the blood. Typically, centrifugation isemployed to separate the component from the blood. The separatedcomponent may be returned to the donor, or collected for a later use,such as a transfusion.

There are a variety of apheresis procedures, which may be generallyclassified according to the particular component to be separated and/orthe method of separation. For example, the separation of plateletsduring apheresis is known as plateletpheresis or thrombocytapheresis,the separation of young red blood cells is known as neocytapheresis, andthe separation of plasma is known as plasmapheresis.

With respect to classification by the mode of separation, among thoseprocedures are methods including continuous flow, and intermittent flow.Typically, during continuous flow, blood is withdrawn from a donor fromone venipuncture site using a pump, processed to separate at least onedesired component, and the component depleted blood is returned to thedonor through a second venipuncture site, essentially simultaneously,using an additional pump.

Typically, during intermittent flow, which utilizes a singlevenipuncture site, blood is withdrawn from an individual using a pump,and the blood is processed to separate at least one component. The pumpis then reversed to return the component depleted blood to the donor.These cycles of withdrawal and return may be repeated as necessary untilthe desired amount of separated component is obtained. For example,during intermittent flow plateletpheresis, there may be several cyclesof withdrawal of blood from the donor and separation ofplatelet-containing fluid from the blood, followed by return of theplatelet-depleted red cell-containing blood, to the donor, to obtain atherapeutic dose of platelets.

Continuous flow and intermittent flow apheresis protocols may includecentrifugation, and those techniques including centrifugation aretypically referred to as continuous flow centrifugation (CFC), andintermittent flow centrifugation (IFC), respectively. Typically, duringthese protocols, blood may be spun in a centrifuge bowl and/or exposedto a rotating membrane to separate the desired component(s).

There are a number of drawbacks associated with apheresis systems,particularly with respect to processing the separated component. Forexample, during continuous flow and intermittent flow plateletpheresis,since a limited volume of blood may be withdrawn from the donor at anygiven time, some methods include accumulating or pooling the separatedplatelets until almost the entire procedure, i.e., the separation of thedesired amount of platelets, is complete. The apheresis system is thendisconnected from the donor, and the accumulated platelets may beleukocyte depleted, e.g., by passage through a leukocyte depletiondevice. This is a time consuming, inefficient process, in that extratime is required to leukocyte deplete the large quantity of accumulatedplatelets after plateletpheresis is completed. Similar drawbacks areassociated with other apheresis protocols, e.g., involving accumulatingand leukocyte depleting other components, such as red cells and/orplasma.

Among other disadvantages, the leukocyte depletion of the accumulatedcomponent, e.g., platelets, requires the use of a correspondingly largerleukocyte depletion device to obtain a desired leukocyte depletionefficiency in an acceptable amount of time. Furthermore, due to itslarger size, the device may hold up an increased amount of valuableplatelets which may be difficult to recover in a cost effective manner.

Additionally, the presence of air or gas, for example, in a containerwith the separated component, in the fluid flow path of the separatedcomponent and/or in the component fluid itself, may adversely affectprocessing efficiency and/or impair the quality of the component and maydecrease its storage life. For example, since the platelet containingfluid may displace gas as it passes from one location to another, it maybe difficult and/or time consuming to efficiently pass the fluid througha porous medium such as a leukocyte depletion medium, since thedisplaced gas may block the medium. Similarly, since the plateletcontaining fluid may be "foamy," i.e., include air bubbles, the presenceof air may present difficulties when the fluid is to be passed through aporous medium such as a leukocyte depletion medium. Moreover, oxygen maybe associated with an increased metabolic rate (during glycolysis),which may lead to decreased storage life and decreased viability andfunction of blood components such as red cells and/or platelets. Thus,it may be desirable to minimize the presence of air when bloodcomponents are being processed and/or before the blood components arestored, particularly when they are to be stored for long periods oftime, e.g., several days or more.

Accordingly, there is an unaddressed need in the art for providingleukocyte depletion during apheresis, thereby decreasing the time neededto separate and leukocyte deplete a blood component. There is also aneed for a system that provides for minimizing the presence of air whileprocessing the separated component, e.g., while passing the separatedcomponent through a porous medium, and/or for minimizing the presence ofair before storing the separated component.

Moreover, there is a particular need for a system that is compatiblewith existing systems, including automated systems, and provides forseparation of a component of blood, separation of air from the componentflow path, and leukocyte depletion of the component, preferably withoutextending the time that the donor is attached to the processing system.

These and other advantages of the present invention will be apparentfrom the description as set forth below.

SUMMARY OF THE INVENTION

Processes, systems and devices according to the instant inventionprovide for withdrawal of a biological fluid from a source, separationof a component of the biological fluid, return of the component depletedbiological fluid to the source, and leukocyte depletion of a portion ofthe separated component before the return of the component depletedbiological fluid to the source is completed. Preferably, when the sourceof the biological fluid is a donor, the instant invention provides forseparation and leukocyte depletion of a component of a biological fluidsubstantially contemporaneously with the return of the biological fluidto the donor.

The instant invention also provides for separation of a component of abiological fluid and separation of gas from the flow path of a portionof the separated component, before the return of the component depletedbiological fluid to the source is completed. Preferably, when theseparated component flow path includes a porous medium, e.g., a filterassembly including an inlet and an outlet, and a porous mediuminterposed across the flow path between the inlet and the outlet, theinstant invention provides for separation of gas from the fluid flowpath of the separated component upstream of the porous medium, i.e., sothat gas neither contacts nor passes through the porous medium.

The instant invention may be used in a semi-automated or automatedsystem, and provides for the separation of gas from the flow path of theseparated component, and for efficient leukocyte depletion of theseparated component.

In accordance with the invention, the separated component may beleukocyte depleted while the remaining component depleted biologicalfluid is being returned to the donor. This eliminates or decreases thetime required for post apheresis leukocyte depletion, since theseparated component, e.g., platelets, may be leukocyte depleted whilethe remaining biological fluid, for example, red cell containingplatelet-depleted fluid, may be returned to the donor.

Since the separated component need not be accumulated before leukocytedepletion, the leukocyte depletion device can be smaller, resulting in acost savings since less valuable fluid is "lost" due to fluid hold up ofthe smaller device. Moreover, there may be an additional cost savingsresulting from the use of smaller devices.

Additionally, leukocyte depletion efficiency can be increased by, forexample, controlling the flow rate of fluid through the leukocytedepletion device, without additionally inconveniencing the donor, sinceleukocyte depletion of the separated component can be performedsubstantially contemporaneously with the return of the componentdepleted fluid toward the donor. Thus, for example, a decreased flowrate of the separated component through the leukocyte depletion deviceneed not extend the time that the donor remains attached to the system,since the flow rate of the component depleted fluid back to the donormay remain unchanged.

The instant invention is particularly useful when there are a pluralityof donors to be sequentially connected to the apheresis system, e.g., ata donation center, since it minimizes the time that the machine will beunavailable between donations. Since biological fluid must be clearedfrom the apheresis system before it can be connected to the next donor,the present invention, in which leukocyte depletion of the separatedcomponent may be essentially completed as the system is disconnectedfrom the donor, minimizes the amount of fluid to be cleared from theapheresis system between donations. As a result, less time is requiredto clear the system before the next donation.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an embodiment of the present invention including a gasseparation arrangement and a filter assembly.

FIG. 2 is another embodiment of the present invention.

FIG. 3 is another embodiment of the present invention.

FIG. 4 is an embodiment of the present invention including a gasseparation arrangement and a filter assembly, as well as a gascollection and displacement loop.

SPECIFIC DESCRIPTION OF THE INVENTION

A method in accordance with the invention comprises processing abiological fluid through one or more cycles of: obtaining biologicalfluid from a source, separating at least one component from thebiological fluid, and returning the component depleted biological fluidto the source; and, while processing the biological fluid, at least oneof (1) separating gas from the flow path of the separated component bypassing a portion of the separated component through a gas separationarrangement and (2) passing a portion of the separated component througha leukocyte depletion medium.

A method in accordance with the invention includes obtaining abiological fluid from a source, separating at least one component fromthe biological fluid, passing the component depleted biological fluidtoward the source of the biological fluid while leukocyte depleting aportion of the separated component by passing the separated componentthrough a leukocyte depletion medium.

The present invention also provides a method for processing a biologicalfluid including obtaining a biological fluid from a source, separatingat least one component from the biological fluid, passing the componentdepleted biological fluid toward the source of the biological fluidwhile passing a portion of the separated component into a gas separationarrangement to separate gas from the flow path of the separatedcomponent.

In a more preferred embodiment, a method in accordance with the presentinvention includes separating gas from the flow path of the separatedcomponent and depleting leukocytes from a portion of the separatedcomponent, while returning the component depleted biological fluid tothe source.

The present invention also provides a system comprising a conduit havinga first end suitable for providing fluid communication with a componentseparation device, and a second end suitable for providing fluidcommunication with a receiving container; and, interposed between thesecond end of the conduit and the receiving container, at least one of agas separation arrangement and a leukocyte depletion device.

In accordance with the invention, a system is provides comprising afirst container for holding a separated leukocyte containing componentof a biological fluid; a second container for holding a separatedleukocyte depleted component of a biological fluid; a gas separationarrangement including a porous medium; and, a filter assembly comprisinga leukocyte depletion medium; said gas separation arrangement and saidfilter assembly interposed between the first container and the secondcontainer.

In accordance with the invention, biological fluid includes any treatedor untreated fluid associated with living organisms, particularly blood,including whole blood, warm or cold blood, and stored or fresh blood;treated blood, such as blood diluted with a physiological solution,including but not limited to saline, nutrient, and/or anticoagulantsolutions; one or more blood components, such as platelets suspended inplasma, platelet concentrate (PC), platelet-rich plasma (PRP),platelet-free plasma, platelet-poor plasma (PPP), plasma, packed redcells (PRC), transition zone material, buffy coat; analogous bloodproducts derived from blood or a blood component or derived from bonemarrow; red cells suspended in physiological fluid; and plateletssuspended in physiological fluid. The biological fluid may includeleukocytes, or may be treated to remove leukocytes. As used herein,biological fluid refers to the components described above, and tosimilar blood products obtained by other means and with similarproperties.

A biological fluid processing system according to the invention iscompatible with a wide variety of component separation systems and/orcomponent separation devices. Thus, a biological fluid processing systemas disclosed herein may be placed in fluid communication with, forexample, an apheresis system including a separation device forseparating at least one component from a biological fluid.

Typically, the biological fluid processing system includes at least oneof a gas separation arrangement and a filter assembly comprising aleukocyte depletion device, in fluid communication, via at least oneconduit, with at least one container. Generally, the system includes twoor more conduits, and at least one conduit is suitable for providingfluid communication with the component separation device. Morepreferably, a biological fluid processing system for connection to aseparation device in accordance with the invention includes at least twocontainers, with a gas separation arrangement and a filter assemblyinterposed between the containers.

In the embodiment illustrated in FIG. 1, which includes an apheresisseparation system 90 including a component separation device 1, theseparation device is in fluid communication with a biological fluidprocessing system 10. The illustrated biological fluid processing system10 includes a conduit 20 having a first end and a second end, whereinthe ends are suitable for fluid communication with both the separationsystem, and another element of the biological fluid processing system.In another embodiment, the apheresis separation system 90 includes aconduit for providing fluid communication with both the apheresis system90 and an element of the biological fluid processing system 10.

In the embodiment illustrated in FIG. 1, one end of conduit 20 is influid communication with at least one container 2, such as a holdingcontainer. Downstream of the holding container 2 is a filter assembly 6and another container 7, such as a receiving or collection container. Inthis illustrated embodiment, which includes conduits 30, 40, and 50, andprovides for separation of gas from the flow path of the separatedcomponent of the biological fluid, the biological fluid processingsystem 10 includes a gas separation arrangement 100 comprising a gascollection device 4 such as a drip chamber and a gas separation device 3such as a vent, which are interposed between the holding container 2 andthe filter assembly 6.

The system may include at least one flow control device such as a clampassociated with at least one conduit and/or container. In theillustrated embodiments, the biological fluid processing system includesflow control device 5. Preferably, as shown in the illustratedembodiments, the flow control device 5 is interposed between the gasseparation arrangement 100 and the filter assembly 6. In the embodimentillustrated in FIG. 4, the system includes additional flow controldevices 210, 220, 230 and 240.

The biological fluid processing system may include a gas collection anddisplacement loop which preferably includes at least one conduit, and atleast one of a gas collection and displacement container and a liquidbarrier medium. In another embodiment, the system may include a samplingarrangement, which preferably includes at least one conduit and asatellite container such as a sampling container.

In the embodiment illustrated in FIG. 4, the system includes a gascollection and displacement loop 200, which includes a gas collectionand displacement container 207, a liquid barrier assembly 203, andconduits 250, 260, and 270. Preferably, at least one flow control devicesuch as a clamp may be associated with the gas collection anddisplacement loop 200. In the illustrated embodiment, flow controldevices 230 and 240 associated with conduits 270 and 250, respectively,of the gas collection and displacement loop 200.

Each of the components or elements of the invention will now bedescribed in more detail below.

As illustrated in the Figures, e.g., FIG. 1, an apheresis separationsystem 90 including a separation device 1 may be used to separate atleast one component from a biological fluid.

A variety of devices and/or systems for separating at least onecomponent from a biological fluid are suitable for carrying out theinvention. These devices and/or systems may provide for separationwithout centrifugation, e.g., by exposing the biological fluid to aporous separation medium such as a planar sheet or a bundle of hollowfibers, and/or they may provide for separation by centrifugation,including intermittent or continuous centrifugation. While a number ofdevices and systems are suitable, the preferred embodiment includes theuse of commercially available devices and systems known to those ofordinary skill in the art. Exemplary devices and systems include, butare not limited to, those made by Haemonetics Corporation; FenwalLaboratories; Cobe Laboratories; Asahi Medical Co., Ltd.; BaxterInternational, Inc., and Baxter Travenol Laboratories, Inc. Preferably,the separatory device 1 is an intermittent flow centrifugation (IFC)device, such as is conventionally used in the art. The biological fluidprocessing system according to the invention may include the componentseparation system and/or device.

Typically, the component separation system 90 provides for movement ofthe fluid by maintaining a pressure differential sufficient to cause thefluid to move from one location to another. For example, the componentseparation system may include, but is not limited to, at least one pump,such as a reversible or a non-reversible pump, to establish the pressuredifferential. In other embodiments, the pressure differential may beestablished by, for example, gravity head, using an expressor such as amechanical, pneumatic or hydraulic expressor, by applying pressure byhand or with a pressure cuff, or by creating a vacuum.

While the component separation device and/or system may be manuallycontrolled, the preferred embodiment is compatible with semi-automatedor fully automated biological fluid processing operations. For example,using a microprocessor controlled device or system, once a source of abiological fluid such as a container or a donor is connected to thedevice and/or system, an appropriate sequence may be selected, and bloodmay be, automatically, withdrawn, the desired component(s) separated,and the component depleted biological fluid returned to the source. Arepresentative example of such an automated system is a HaemoneticsModel MCS Plus® apheresis system (Haemonetics Corporation, Braintree,Mass.).

In some embodiments, as will be noted in more detail below, at least oneof leukocyte depletion of the separated component and separation of gasfrom the flow path of the separated component may also be under semi- orfully automated control.

GAS SEPARATION ARRANGEMENT

In accordance with the invention, the biological fluid processing system10 may include a gas separation arrangement 100 to collect gas that maybe present in the system and/or to separate gas from a biological fluidor from the flow path of the biological fluid. The gas separationarrangement 100 may separate gas from a biological fluid processingsystem. In some embodiments, the gas separation arrangement 100 mayallow gas into the biological fluid processing system. As noted in moredetail below, the gas separation arrangement may be used to minimize orprevent gas from reaching a filter assembly 6 such as a leukocytedepletion assembly and/or to minimize or prevent gas from reaching adownstream container 7 such as a receiving or collection container. Thegas separation arrangement 100 may also be used for maximizing recoveryof the biological fluid. In a sterile system, the gas separationarrangement 100 should provide for maintaining the sterility of thesystem.

The gas separation arrangement 100 includes at least one of a gascollection device and a gas separation device. Preferably, the gasseparation arrangement 100 includes at least one gas collection deviceand at least one gas separation device.

In a preferred embodiment, the gas separation arrangement includes atleast one porous element that allows gas to pass through the element,without the separated component passing through the element.

The placement of the gas separation arrangement 100 may be optimized toachieve a desired result. In a preferred embodiment, the gas separationarrangement 100 is located upstream of the filter assembly 6.

In accordance with the invention, the gas separation arrangement 100 mayinclude a gas collection device 4 such as a drip chamber. The gascollection device 4 may be used to prevent gas from reaching a filterassembly 6 such as a leukocyte depletion assembly and/or to prevent gasfrom reaching a container 7 downstream of the gas collection device. Thegas collection device 4 may be used to collect gas that is present inthe system, and/or to separate gas from the flow path of a biologicalfluid. In some embodiments, the gas collection device may be used formaximizing recovery of the biological fluid.

The drip chambers which may be used in the biological fluid processingassembly may be constructed of any material compatible with biologicalfluid and gas. A wide variety of these drip chambers are already knownin the art. The size of the drip chamber may be varied depending on, forexample, the volume of fluid to be passed into the drip chamber and/orthe number of cycles of processing.

The gas separation arrangement 100 may include at least one structure,device or element, preferably including a porous medium, that allows gasto be separated from a biological fluid being processed and/or to beseparated from the flow path of the biological fluid being processed,e.g., allows gas out of a biological fluid processing system, butresists the passage of biological fluid. The gas separation arrangement100 may also include at least one structure, device or element, thatallows gas into a biological fluid processing system.

In a preferred embodiment, the gas separation arrangement 100 includesat least one gas separation device 3 such as a vent, more preferably agas outlet, to improve the efficiency of gas separation from thebiological fluid and/or from the flow path of the biological fluid. Insome embodiments, at least one vent may be used to maximize the recoveryof biological fluid in the downstream container. The gas separationdevice 3 should be chosen so that the sterility of the system is notcompromised.

In a preferred embodiment, a vent such as a gas outlet allows gas thatmay be present in a biological fluid processing system out of thesystem. Thus, the gas outlet may provide for minimizing the volume ofgases that remain in, or in contact with, a biological fluid duringprocessing. In one embodiment, the gas outlet may also allow gas intothe biological fluid processing system, and thus may function as a gasinlet.

The gas outlet comprises at least one porous medium, hereinafterreferred to as a porous element, designed to allow gas to passtherethrough. A variety of materials may be used, provided the requisiteproperties of the porous element are achieved. These properties includethe necessary strength to handle the differential pressures encounteredin use and the ability to provide the desired permeability without theapplication of excessive pressure.

The gas outlet should be chosen so that the sterility of the system isnot compromised. For example, the porous elements of the gas outletshould preferably have a bacterial blocking pore rating, e.g., of about0.2 micrometer or less, to preclude bacteria entering the system.

Preferably, the gas outlet includes at least one liquophobic porouselement. Because the liquophobic porous element is not wettable, orpoorly wettable, by the biological fluid being processed in the system,gas in the system that contacts the liquophobic element will passthrough it, and the biological fluid that is present will contact theelement, but will not pass through.

The gas outlet may include at least one liquophilic porous element, thatallows gas to exit, but, once the element is wetted with biologicalfluid, does not allow gas to enter, the system. Preferably the gasoutlet includes both a liquophobic porous element and a liquophilicporous element. In a preferred embodiment of the invention, the outletincludes at least one liquophobic membrane and at least one liquophilicmembrane, and the outlet allows gas to pass through the liquophilicmembrane and then the liquophobic membrane until the liquophilicmembrane is wetted by the biological fluid, at which time gas flowautomatically stops, without biological fluid passing through theoutlet.

Additionally, the gas outlet may include a housing, which may include acap or closure. Exemplary gas outlets, and processes for using them areas disclosed in International Publication Nos. WO 91/17809 and WO92/07656, and U.S. Pat. Nos. 5,126,054 and 5,217,627.

The components of the gas separation arrangement 100 and/or theconfiguration of the arrangement may be optimized to achieve a desiredresult. For example, in those embodiments including at least one gascollection device 4 such as a drip chamber, and at least one gasseparation device 3 such as a gas outlet, the gas outlet is preferablylocated upstream of the drip chamber. In a preferred embodiment, the gasoutlet is in communication with an anterior or upstream portion of thedrip chamber. The gas outlet may be integrally connected to the dripchamber. Preferably, the gas outlet is located where gas is likely to becollected during processing, e.g., at or near the highest point of thedrip chamber.

The gas separation arrangement 100 may include additional elements, suchas, for example, at least one of a conduit, and a defoaming element.

FILTER ASSEMBLY

The biological fluid processing system 10 may include at least onefilter assembly 6, i.e., a housing including an inlet and an outlet, anddefining a flow path between the inlet and the outlet, with at least oneporous medium interposed between the inlet and the outlet. In a morepreferred embodiment, the filter assembly 6 comprises a leukocytedepletion device, and the porous medium comprises a leukocyte depletionmedium.

A leukocyte depletion medium which may be used in accordance with thepresent invention comprises a porous medium suitable for depletingleukocytes from the fluid passing through the leukocyte depletionmedium. Exemplary leukocyte depletion media include but are not limitedto those disclosed in U.S. Pat. Nos. 5,217,627, 5,100,564 and 4,880,548as well as International Publication Nos. WO 92/07656 and WO 91/04088.Additional exemplary leukocyte depletion media include those disclosedin U.S. Pat. Nos. 4,925,572, 4,923,620, and 5,229,012. These U.S.patents and International Publications also disclose exemplary housingsfor the leukocyte depletion media.

The containers which may be used in the biological fluid processingsystem may be constructed of any material and shape compatible withbiological fluid and gas. A wide variety of these containers are alreadyknown in the art. For example, blood collection and satellite bags aretypically made from plasticized PVC, e.g. PVC plasticized withdioctylphthalate, diethylhexylphthalate, or trioctyltrimellitate. Thebags may also be formed from a polyolefin, polyurethane, polyester, or apolycarbonate.

As used herein, fluid communication may be established by any structurewhich allows the biological fluid and/or gas to pass from one locationto another, such as by at least one conduit or tube. A flow controldevice such as a clamp, seal, valve, transfer leg closure, or the like,may be located within or on at least one of the conduits and/or thecontainers. The conduits used in the instant invention may beconstructed of any material compatible with biological fluid and gas.Preferably, they may be composed of a flexible material, such aspolyvinyl chloride (PVC), or plasticized PVC, e.g., PVC plasticized withdioctylphthalate, diethylhexylphthalate, or trioctyltrimellitate.

In accordance with the invention, the biological fluid processing system10, which may be closed and/or sterile, may include additional elementsor components, such as, but not limited to, at least one of a conduit, aconnector, an injection port, and a container. The system may alsoinclude, for example, at least one vent such as a gas outlet, asdescribed earlier, and/or at least one inlet.

For example, the biological fluid processing system may include a gasinlet to allow gas into the system. The gas inlet may allow gas into thesystem for maximizing recovery of the biological fluid. In a preferredembodiment, the gas inlet allows gas into the system so that separatedcomponent retained or entrapped in at least one element of the systemcan be recovered. In a sterile system, the gas inlet should provide formaintaining the sterility of the system. In one embodiment, the gasinlet comprises a porous element, more preferably, a porous elementhaving a pore rating that blocks the entry of bacteria, e.g., a porerating of about 0.2 micrometer or less.

Additionally, the gas inlet may include a housing, which may include acap or closure. Exemplary gas inlets, and processes for using them areas disclosed in International Publication Nos. WO 91/17809 and WO92/07656, and U.S. Pat. No. 5,217,627.

Preferably, the biological fluid processing system includes a samplingarrangement comprising at least one conduit and at least one additionalcontainer, such as a sampling container. In a more preferred embodiment,the sampling arrangement is in fluid communication with receivingcontainer 7, and comprises a sampling container and at least oneconduit, with the conduit providing fluid communication between thereceiving container 7 and the sampling container.

In accordance with the invention, the biological fluid processing system10 may include a gas collection and displacement loop 200 to collectgas, and optionally, to allow sampling of the separated component. Insome embodiments, the collected gas may be used to recover additionalbiological fluid. In a preferred embodiment, the gas collection anddisplacement loop provides a safeguard that the separated componentcontaminated with leukocytes will be isolated from the leukocytedepleted separated component, since the contaminated fluid will not passthrough at least one of the liquid barrier medium and the gas collectionand displacement container, and into the receiving container 7.

The gas collection and displacement loop 200 includes at least oneconduit, 250, 260, and/or 270, and at least one of a liquid barrierassembly 203 and a gas collection and displacement container 207. Theliquid barrier assembly 203 comprises a housing including a porousliquid barrier medium that allows gas to pass through but bars thepassage of liquid. Preferably, at least one flow control device, 230and/or 240, is associated with at least one conduit of the gascollection and displacement loop.

In a preferred embodiment, as illustrated in FIG. 4, the gas collectionand displacement loop 200 includes conduits 250, 260 and 270, liquidbarrier assembly 203, and gas collection and displacement container 207.In the illustrated embodiment, the gas collection and displacement loop200 is placed in fluid communication with the other components of thebiological fluid processing system 10 via connectors 280 and 290.Preferred gas collection and displacement loops and methods for usingthem are disclosed in International Publication No. WO 93/25295.

In one embodiment, a method in accordance with the invention includesobtaining a biological fluid, typically including red cells, plasma, andplatelets, from a source, separating at least one component, forexample, platelets, from the biological fluid, returning the componentdepleted biological fluid to the source, and initiating furtherprocessing of the separated component, preferably before the return ofthe component depleted fluid to the source is completed. Furtherprocessing of the separated component includes at least one ofseparation of gas from the flow path of the component, preferably bypassing the separated component through a gas separation arrangement,and leukocyte depletion of the component, preferably by passing thecomponent through a leukocyte depletion device.

In accordance with the invention, the biological fluid may be processed,e.g., obtained from the source, the desired component separated, and thecomponent depleted biological fluid returned to the source, two or moretimes. For example, in those embodiments wherein the source is a donor,the obtaining, separation and return as described above is preferablyrepeated at least twice during the apheresis period, i.e., the periodbetween connecting the donor to the separation system 90, anddisconnecting the donor.

The method may also include introducing gas into the separated componentfluid flow path, e.g., to recover separated component trapped orentrained in at least one element of the biological fluid processingsystem.

Typically, the biological fluid is commingled with an additive fluid,for example, an anticoagulant, as is known in the art. Preferably, thebiological fluid, e.g., whole blood, is commingled with an anticoagulantbefore the desired component is separated from the biological fluid. Ina less desirable embodiment, the biological fluid may be mixed with anadditive fluid and passed through a leukocyte depletion device beforethe desired component is separated from the biological fluid.

A variety of methods for withdrawing a biological fluid from a source,separating a desired component from the biological fluid, and returningthe component depleted biological fluid to the source are known in theart. In the illustrated embodiment, a source of biological fluid, whichmay be a container of biological fluid, but is more preferably a donorsuch as a human or an animal, is connected to a separation system 90which includes a component separatory device 1, so that at least onecomponent of the biological fluid may be separated from the biologicalfluid. For example, a conventional apheresis system, more preferably acentrifugation system, even more preferably an intermittent flowcentrifugation (IFC) system, may be connected to a donor and operated asis known in the art. In a more preferred embodiment, the method includesautomatically withdrawing the biological fluid, separating the desiredcomponent from the biological fluid, and returning the componentdepleted biological fluid to the source.

Once separated from the biological fluid, the component is furtherprocessed, which includes separating gas from the flow path of thecomponent and/or leukocyte depleting the component. For example, theseparated component may be passed from the separation device 1 throughat least one of a gas separation arrangement 100 and a filter assembly 6such as a leukocyte depletion device. The processed component may thenbe collected in a container 7 such as a satellite bag or a receivingcontainer. In some embodiments, the method includes automaticallycontrolling the flow of the separated component to provide for at leastone of separating gas from the flow path of the separated component andleukocyte depleting the separated component. For example, once theappropriate sequence is selected by the operator, a microprocessor maycontrol the flow of the separated component by closing and opening flowcontrol device 5.

For convenience, the separated component will hereinafter be referred toas "the platelets", the "platelet containing fluid", or the "plateletssuspended in plasma", but the invention is not to be so limited. Theplatelets may be passed from separation system 90 into biological fluidprocessing system 10 via conduit 20. The platelets may be passeddirectly to gas separation arrangement 100 as illustrated in FIGS. 2 and3, or they may be passed directly to a filter assembly (not shown).Preferably, however, as shown in FIG. 1, the platelets are first passedto a container 2, such as a holding container, before passing them intothe gas separation arrangement 100 and/or through a filter assembly 6such as a leukocyte depletion device. In a less desirable embodiment,the platelet containing fluid may be passed though a filter assembly 6before passing the fluid to container 2.

In some embodiments, e.g., including the use of a holding container, itmay be desirable to decrease the presence of residual air or gas in theholding container before passing the platelets to the gas separationarrangement 100 and/or the filter assembly 6. In other embodiments,platelets may be passed to the holding container 2 and then to the gasseparation arrangement 100 and/or the filter assembly 6 withoutdepleting gas from the holding container. In an exemplary method fordecreasing the presence of gas in the holding container, a vent such asa gas outlet may be interposed between the component separation system90 and the holding container 2, or the vent may be located in or onholding container 2. In these embodiments, residual gas in the container2 may be removed by passing at least a portion of the gas through thegas outlet before passing platelets into the container 2 and then towardthe gas separation arrangement 100. For example, the vent may be openedand the holding container 2 may be compressed, preferably while flowcontrol device 5 is closed, to pass gas through the gas outlet tominimize the presence of air before closing or clamping the vent andthen passing the platelets into the container 2. Preferably, gas ispassed through the vent while maintaining the sterility of the system.

With respect to FIG. 1, at least one flow control device 5 such as aclamp may be used to control the flow of the platelets. Preferably, flowcontrol device 5 is initially closed, and the platelets suspended inplasma are passed from the holding container 2 toward the gas separationarrangement 100, which drives gas ahead of the separated component intothe gas separation arrangement 100, where gas is separated from theplatelet flow path, e.g., gas is collected in the gas separationarrangement 100. In a preferred embodiment, gas is collected in gascollection device 4 and passed through gas separation device 3.

In those embodiments wherein gas collection device 4 is a drip chamber,gas driven ahead of the platelets is collected in the drip chamberand/or gas bubbles are coalesced in the drip chamber. In a morepreferred embodiment, wherein gas collection device 4 is a drip chamberand gas separation device 3 is a gas outlet, the method includes fillingthe drip chamber with gas displaced by the platelets. Collected gasrises to the upper portion of the drip chamber. The gas outlet may beactivated, e.g., uncapped, or a clamp between the gas outlet and thedrip chamber is opened, and gas then passes through the gas outlet, andplatelets pass into the drip chamber. In a more preferred embodiment,the gas outlet lacks a cap, and there is no clamp between the outlet andthe drip chamber, so that gas passes through the gas outlet and the dripchamber fills with platelets without uncapping or unclamping.

While the passage of gas through the gas separation device 3 may bemanually stopped, e.g., by capping or clamping, in a preferredembodiment, the gas separation device 3 comprises a gas outlet whichincludes a porous element that allows gas to pass therethrough until theelement is wetted by the platelet containing fluid, and gas flow stopsautomatically, without capping or clamping.

Once the flow of gas through the gas outlet is terminated, flow controldevice 5 may be opened, manually or automatically, and plateletcontaining fluid will pass from gas separation arrangement 100 throughconduit 40 into the downstream container or receiving bag 7. In apreferred embodiment, as illustrated in FIGS. 1 and 2, a filter assembly6 such as a leukocyte depletion device is interposed between the gasseparation arrangement 100 and the container or receiving bag 7. Onceflow control device 5 is opened, platelets pass through a leukocytedepletion device and the leukocyte depleted platelets then pass into thedownstream container or receiving bag 7.

Preferably, the method comprises an apheresis period including more thanone complete biological fluid processing cycle of withdrawal ofbiological fluid, and component separation followed by the return of thecomponent depleted biological fluid to the source. For example, theapheresis period in accordance with the invention typically includesabout six to about eight complete cycles. These cycles may beautomatically controlled.

Typically, the separation of gas from the flow path of the platelets,and/or the leukocyte depletion of the platelets, begins or is initiatedduring each cycle, e.g., while the platelets are being separated fromthe biological fluid, or, more preferably, while the remaining plateletdepleted biological fluid, e.g., red blood cell containing fluid, isbeing returned toward the source of the fluid, e.g., the donor. In someembodiments, the separation of gas from the platelets, and/or theleukocyte depletion of the platelets, is completed or essentiallycompleted during each cycle, e.g., while the platelet depletedbiological fluid is returned to the source of the fluid.

In yet another embodiment, the separation of gas from the platelet flowpath, and/or the leukocyte depletion of the platelets, is initiatedduring different cycles within the apheresis period. For example,platelets may be accumulated, e.g., in a container such as a holdingcontainer, during two or more cycles, and platelet depleted biologicalfluid may be returned to the source during each of these cycles.However, further processing of the accumulated platelets may beinitiated later in the apheresis period, i.e., before a later cycle ofreturn of the platelet depleted biological fluid to the source iscompleted. The method may include repeatedly accumulating the separatedcomponent during a plurality of cycles and further processing theaccumulated component during a later cycle in the apheresis period.

Typically, in those embodiments including more than one cycle and theuse of a gas separation arrangement 100, more gas may be separated inthe gas separation arrangement during the first cycle than in subsequentcycles. For example, since the holding container 2, and/or the conduits20, 30 may include air, the passage of platelets in the system duringthe first cycle may displace this air into the gas separationarrangement 100, where it may be separated from the platelet fluid flowpath, e.g., to prevent gas from passing into the filter assembly 6.During subsequent cycles, since air has already been displaced fromvarious elements of the system, less additional air may have to beseparated from the platelet flow path.

Generally, in those embodiments including more than one cycle and theuse of a gas separation arrangement 100 including a drip chamber and agas outlet that automatically stops the flow of gas once the porouselement of the gas outlet is wetted, the gas outlet is utilized and thedrip chamber is filled during the first cycle, e.g., until the elementin the outlet is wetted with biological fluid. In this embodiment, whilethe drip chamber is preferably utilized during subsequent cycles, i.e.,including passing the separated platelets to a receiving container, thegas outlet is preferably not utilized during these cycles. Accordingly,the drip chamber provides for gas collection and gas separation duringthese subsequent cycles.

In a more preferred aspect of this embodiment of the invention, asillustrated in FIG. 1, the gas separation arrangement 100 is locateddownstream of holding container 2, and the gas separation arrangementmay be utilized during the first cycle as noted above. Thus, after flowcontrol device 5 is closed, platelets are passed from container 2 (whichis preferably a flexible container), through conduit 30, into gasseparation arrangement 100. The drip chamber fills, gas passes throughthe gas outlet until the porous element in the outlet is wetted and gasflow through the outlet stops. Flow control device 5 is then opened, andplatelets pass into conduit 40 and through filter assembly 6 intocontainer 7. Preferably, in those embodiments wherein holding container2 is a flexible container, once container 2 has drained, the inner wallsof the container contact one another, e.g., near the connection toconduit 30, sealing the fluid flow path between the container 2 and theconduit 30, thus stopping the flow of platelets without closing flowcontrol device 5.

During subsequent cycles, which allow additional platelets to flow intoand out of container 2, flow control device 5 may remain open, since theflow of platelets may automatically be terminated once the inner wallsof container 2 contact each other. Generally, since less air should bepresent during subsequent cycles, little air will pass from thecontainer 2 into conduit 30 during subsequent cycles. Accordingly, thedrip chamber provides for separation of gas from the platelet flow pathduring these subsequent cycles, so that little or no air will enter thefilter assembly 6.

In other embodiments, including a drip chamber and a gas outlet thatdoes not stop the flow of gas once the porous element is wetted, the gasoutlet and the drip chamber may be utilized during these additionalcycles. Accordingly, the gas outlet may be activated, e.g.,uncapped/unclamped, or inactivated, e.g., capped/clamped, as isdesirable during the method. For example, the gas outlet is activatedwhenever it is desirable to pass gas through the outlet, and the outletis inactivated otherwise. Preferably, in those embodiments including theuse of a holding container, the gas outlet may be utilized during thefirst cycle, and the drip chamber may be utilized during all of thecycles, as described previously.

Thus, in those embodiments including a plurality of cycles, asadditional platelet containing fluid is separated from the biologicalfluid and passed to the receiving container 7, gas may be separated fromthe platelet flow path during passage through the drip chamber 4. Thesize of the drip chamber may be varied depending on the volume ofplatelet containing fluid to be processed and/or the number of cycles ofprocessing.

The platelet containing fluid passes through a separate and isolatedflow path than the unseparated biological fluid and the plateletdepleted biological fluid. Movement of the platelet containing fluidthrough the system may be effected by maintaining a pressuredifferential between elements of the system, e.g., wherein one elementcontains the platelet fluid and another element is the intendeddestination of the fluid. For example, a pressure differential may becreated between receiving container 7 and either one end of conduit 20(e.g., at separation device 1 in an embodiment without holding container2), or holding container 2, so as to cause the fluid to flow in adesired direction, i.e., toward the receiving container. The pressuredifferential may be automatically controlled, or it may be manuallycontrolled.

Preferably, the pressure differential allows the platelet containingfluid to pass from one location to another at a rate independent of theflow rate of the unseparated biological fluid (e.g., as the unseparatedbiological fluid passes from the source to the component separationdevice 1) and/or the flow rate of the platelet depleted biological fluid(e.g., as it passes from the component separation device 1 toward thesource).

For example, fluid may be passed from the source to the separationdevice and/or passed from the separation device to the source at a flowrate of greater than about 35 ml/minute, e.g., about 50 to about 80ml/minute during plateletpheresis, or about 50 to about 150 ml/minuteduring separation of red cells. However, in accordance with theinvention, once the platelet containing fluid has been separated fromthe biological fluid, a pressure differential may be created, e.g., agravity head between the holding container 2 and the receiving container7, and the platelet containing fluid may be passed through the filterassembly 6 at a flow rate of less than about 25 ml/minute. In thoseembodiments wherein the filter assembly is a leukocyte depletionassembly, this slower rate provides for more efficient leukocytedepletion, since, for example, more of the platelet containing fluid maycontact the leukocyte depletion medium. In a more preferred embodiment,the platelets may be passed through the leukocyte depletion device at aflow rate in the range of, for example, about 10 to about 20 ml/minute.

Exemplary methods for creating a pressure differential to allowplatelets to flow through the leukocyte depletion device at thisindependent rate include, but are not limited to, using gravity head, apump, an expressor such as a mechanical, pneumatic or hydraulicexpressor, applying pressure by hand or with a pressure cuff, orcreating a vacuum. For example, with respect to the Figures, thebiological fluid processing system 10 may be arranged such thatreceiving container 7 is placed at the lowest point, and the gravityhead will cause the platelets to flow toward the container 7. In a morepreferred embodiment, as illustrated in FIGS. 1 and 4, holding container2 may be placed above receiving container 7, so that platelets will flowfrom the holding container 2, through the gas separation arrangement 100and the filter assembly 6, into receiving container 7.

In some embodiments, particularly those including passing the plateletsthrough a filter assembly such as a leukocyte depletion device and intoa downstream container, the method includes recovering the valuableplatelets that may remain entrapped in the system once the pressuredifferential is sufficiently decreased. For example, once holdingcontainer 2 (e.g., in FIGS. 1 and 4) and/or conduit 20 (e.g., in FIGS.1, 2 and 4) have sufficiently drained, platelet flow may stop, leavingplatelets in the leukocyte depletion device and/or the conduit upstreamof the leukocyte depletion device. In accordance with the invention, gasmay be added to the platelet fluid flow path to recover additionalplatelet containing fluid.

For example, in a more preferred embodiment, after the final separationcycle, gas may be added to a section of the separated plateletcontaining fluid flow path, so that additional platelets, e.g., in theholding container and/or the leukocyte depletion device, may be passedinto the receiving container. Preferably, the recovery of thisadditional liquid may be essentially completed contemporaneously withthe disconnection of the system from the donor. For example, the donormay be disconnected from the separation system as gas is being added tothe platelet fluid flow path, e.g., at conduit 20, and the flow of thisadditional platelet containing fluid into the receiving container may becompleted shortly thereafter, e.g., about 15 seconds, after the donor isdisconnected from the separation system.

With reference to FIGS. 1 and 4, gas may be introduced into the fluidflow path at any desired location, e.g., upstream of holding container2; upstream of gas separation arrangement 100; within gas separationarrangement 100, e.g., in the drip chamber or through the gas outlet; orbetween the drip chamber and filter assembly 6. Preferably, air isintroduced without compromising the sterility of the system. Exemplarydevices and techniques for the introduction of air include, but are notlimited to, utilizing gas inlets as disclosed in InternationalPublication No. WO 91/17809, and/or utilizing gas collection anddisplacement loops as disclosed in International Publication No. WO93/25295.

For example, a gas inlet as disclosed in International Publication No.WO 91/17809, or one end of a gas collection and displacement loop asdisclosed in International Publication No. WO 93/25295, may beassociated with conduit 20, conduit 30, holding container 2, or gascollection device 4. Before introducing air, but after the finalseparation cycle, platelets suspended in plasma may be passed from theholding container 2, through the gas separation arrangement 100 and thefilter assembly 6, and into receiving container 7, until flow into thereceiving container stops.

In those embodiments including a gas inlet, the inlet, which may beautomatically or manually controlled, may be opened or activated, andadditional platelet containing fluid trapped or retained in the system,e.g., in conduit 20, 30 and/or 40, holding container 2, the dripchamber, and/or in the upstream portion of filter assembly 6, maydrained into the receiving container 7 and recovered.

In those embodiments including a gas collection and displacement loop200, e.g., as illustrated in FIG. 4, gas may be passed through the gascollection and displacement loop and into the platelet fluid flow path,e.g., upstream of the filter assembly 6. For example, since the passageof platelets into receiving container 7 during the first cycle maydisplace gas (e.g., in conduit 50) into the receiving container, thisgas may be passed from the container 7 into the gas collection anddisplacement loop 200. Illustratively, receiving container 7 may becompressed to pass gas, and, optionally, platelets for sampling, throughconnector 280 and conduit 250 into gas collection container 207. Gas maythen be passed from gas collection container 207, through conduit 260,through liquid barrier assembly 203, conduit 270 and connector 290, andtoward filter assembly 6, thus allowing additional platelets to draininto receiving container 7.

Illustratively, with respect to FIG. 4, passing gas through the gascollection and displacement loop 200 and through connector 290 may allowthe drainage of platelets from conduits 30 and 40, as well as from gascollection device 4 and the upstream of filter assembly 6, intocontainer 7. In other embodiments, one end of conduit 270 of the gascollection and displacement loop 200 may be associated with, forexample, conduit 20 or holding container 2, and the passage of gas intothese elements may allow additional platelets to be recovered.

In a preferred embodiment, the platelets may be recovered in container 7and utilized at the appropriate time, e.g., after storage. In someembodiments, for example, in those embodiments including a samplingarrangement instead of a gas collection and displacement loop, a portionof the platelets may be passed from container 7 to an additionalcontainer, the sampling container, so that this sample in the additionalcontainer may be tested before utilizing the platelets in receivingcontainer 7. For example, the system may include a sampling arrangementcomprising a sampling container and at least one conduit providing fluidcommunication between the sampling container and the receiving container7, so that gas and platelets may be passed from the receiving container7 through the conduit and into the sampling container, and the plateletsmay be sampled at the appropriate time.

With respect to utilizing the gas collection and displacement loop forsampling, since gas and platelets may be passed from container 7 intogas collection container 207 of gas collection and displacement loop 200as described above, the gas may then be passed from gas collectioncontainer 207 through liquid barrier assembly 203 into conduit 270 ofthe loop 200, while leaving platelets for sampling in container 207. Thegas passed from the gas collection container 207 may be used to recoveradditional platelets as noted above, and the platelets may be sampled atthe appropriate time. In a preferred embodiment, after a desired amountof platelets for sampling have been passed into gas collection container207, and the displaced gas has been passed through the loop 200 so thatadditional platelets have been recovered in container 7, containers 7and 207, along with conduit 250, are removed from the system, and storeduntil the platelets in container 7 are to be used.

For example, once a sample of platelets has been passed into collectioncontainer 207 and the additional platelets are recovered in container 7,conduit 50 is heat sealed between connector 280 and filter assembly 6,and conduits 250 and 260 are heat sealed, thus allowing the removal, asa unit, of containers 7 and 207 along with conduit 250 interposedbetween the containers.

Further embodiments are encompassed by the present invention. Forexample, in one embodiment, after the desired component, e.g.,platelets, is separated from the biological fluid, the platelet depletedbiological fluid may be passed through a leukocyte depletion devicebefore it is returned to the source. For example, whole blood may beobtained from a donor, and platelets may be separated from the blood.The platelet depleted blood may be passed through a leukocyte depletiondevice, and the blood, depleted of platelets and leukocytes, may bereturned to the donor. In another embodiment, a biological fluid may beobtained from a source and passed through a leukocyte depletion devicebefore the platelets are separated from the biological fluid. In theseembodiments, the separated platelets may be further processed as notedabove, i.e., passed through the gas separation arrangement 100 and/orthe filter assembly 6.

As noted earlier, the separated component is not limited to platelets.Accordingly, in other illustrative embodiments, the separated componentmay be, for example, red cells, and the method may include returning redcell depleted blood to the source, and, during the apheresis period, atleast one of passing red cells to a gas separation arrangement toseparate gas from the flow path of the red cells and leukocyte depletingthe red cells by passing them through a leukocyte depletion medium.

EXAMPLES Example 1

The biological fluid processing system used to perform this exampleincludes a 100 ml plastic container, a 600 ml plastic container, a dripchamber, and a gas outlet, set up in manner that generally correspondsto that described for FIG. 1. The system is arranged generallyvertically, and the 100 ml container, the holding container, is hung ata distance of about 12 inches above the 600 ml container, the receivingcontainer.

The leukocyte depletion assembly, which is produced in accordance withU.S. Pat. No. 4,880,548, is hung at a distance of approximately 4 inchesfrom the holding container. The gas outlet, which is produced inaccordance with International Publication No. WO 91/17809, and includesa porous element that blocks bacteria, and stops the passage of gas oncewetted with biological fluid, is integrally connected to the dripchamber, which is a commercially available 20 ml drip chamber.

The biological fluid processing system is connected to a HaemoneticsModel MCS Plus® apheresis system (Haemonetics Corporation, Braintree,Mass.). Since this apheresis system includes a conduit for passing theseparated component, this conduit is connected to the biological fluidprocessing system via sterile docking.

A manually operable clamp is located on the conduit between the dripchamber and the leukocyte depletion assembly. The clamp is initiallyclosed.

A donor is connected to the Haemonetics Model MCS Plus® apheresis systemand the system is operated according to the manufacturer's instructions.Blood is withdrawn from the donor, mixed with anticoagulant, and passedto the centrifuge at a flow rate of about 60 ml/minute to separateplatelets from the blood. The separated platelets are passed to theholding container.

As platelet-depleted blood is returned to the donor along one flow path,the separated platelets pass along a separate flow path from the holdingcontainer toward the drip chamber, and gas is displaced into the dripchamber. The drip chamber fills with gas, gas passes through the porouselement of the gas outlet, and platelets enter the chamber. The chamberfills with platelets, which eventually contact the porous element of thegas outlet, and gas flow stops, without platelets passing through theporous element.

The clamp between the drip chamber and the leukocyte depletion assemblyis opened. Platelets prime the leukocyte depletion assembly, and passthrough the assembly at a flow rate of about 20 ml/minute, and into thedownstream receiving container. Once the holding container issufficiently emptied, the inner walls of the container contact eachother, and platelet flow stops.

Another cycle of withdrawal of blood from the donor is initiated, andplatelets are separated and passed to the holding container as notedabove. Once sufficient platelets enter the holding container, the innerwalls of the container are spread apart, and platelets flow through thedrip chamber and the leukocyte depletion assembly, and into thereceiving container. While platelet depleted blood is returned to thedonor, the platelets drain out of the holding container. Once theholding container is sufficiently drained, the inner walls contact eachother, and flow stops as described previously.

This withdrawal of blood, separation, return, and passage of plateletsinto the receiving container is repeated four more times, to obtain thedesired amount of platelets. The platelets are found to be highlydepleted of leukocytes, i.e., less than about 5×10⁵ /unit.

Example 2

This Example is set up and performed generally in accordance with thatdescribed in Example 1. However, in this Example, the biological fluidprocessing assembly includes a leukocyte depletion assembly produced inaccordance with U.S. Pat. No. 4,925,572, and the 100 ml holdingcontainer is hung at a distance of about 20 inches above the 600 mlreceiving container. The leukocyte depletion assembly is hung at adistance of approximately 4 inches from the holding container.

Additionally, the Haemonetics Model MCS Plus® apheresis system in thisExample is operated to separate red cells from the blood, rather than toseparate platelets from the blood as described in Example 1.

The withdrawal of blood, separation, return, and passage of theseparated component through the gas separation arrangement and then theleukocyte depletion assembly into the receiving container is generallyperformed as described in Example 1, to obtain the desired amount of redcells. However, the receiving container is hung about 20 inches belowthe holding container in this Example, rather than about 12 inchesbelow, as in Example 1. The red cells pass through the leukocytedepletion assembly at a rate of about 20 ml/minute. The red cells arefound to be highly depleted of leukocytes, i.e., less than about 5×10⁵/unit.

Example 3

The Example is set up and performed generally in accordance with thatdescribed in Example 1. However, the biological fluid processing systemin this Example also includes a sampling arrangement comprising aconduit and a 50 ml plastic container, the sampling container. AY-connector, downstream of the leukocyte depletion assembly, isinterposed between the assembly and the receiving container. One end ofthe conduit of the sampling arrangement is connected to the Y-connector,and the other end of the conduit is connected to the 50 ml samplingcontainer. The sampling arrangement also includes an injection port influid communication with the sampling container. All of the connectionsare via sterile docking.

The platelets are passed into the receiving container as described inExample 1. The receiving container is compressed, passing gas and about20 ml of platelets through the Y-connector and into the samplingcontainer. The conduits between the leukocyte depletion assembly and thereceiving container, and between the Y-connector and the samplingcontainer are heat sealed, and the receiving container and the samplingarrangement are separated as a unit from the rest of the biologicalfluid processing system.

Platelets are withdrawn for sampling via the injection port in fluidcommunication with the sampling container.

While the invention has been described in some detail by way ofillustration and example, it should be understood that the invention issusceptible to various modifications and alternative forms, and is notrestricted to the specific embodiments set forth. It should beunderstood that these specific embodiments are not intended to limit theinvention but, on the contrary, the intention is to cover allmodifications, equivalents, and alternatives falling within the spiritand scope of the invention.

We claim:
 1. A method for processing a biological fluidcomprising:obtaining a biological fluid comprising red blood cells andplatelets from a source; separating red blood cells from the biologicalfluid to deplete the biological fluid of red blood cells; returning redblood cell-depleted platelet-containing biological fluid to the sourcewhile:separating gas from a flow path of the separated red blood cells;and, passing a portion of the separated red blood cells along the flowpath and through a leukocyte depletion medium to deplete leukocytes fromthe red blood cells.
 2. The method of claim 1 wherein the source is adonor, the method including withdrawing biological fluid from the donor,anddepleting leukocytes from the separated red blood cells and returningred blood cell-depleted platelet-containing biological fluid to thedonor substantially contemporaneously.
 3. The method of claim 2 whereinwithdrawing the biological fluid from the donor, separating red bloodcells from the biological fluid, and returning red blood cell-depletedplatelet-containing biological fluid to the donor includes intermittentflow centrifugation.
 4. The method of claim 2 including withdrawingbiological fluid from the donor and returning red blood cell-depletedplatelet-containing biological fluid to the donor at least twice.
 5. Themethod of claim 2 wherein withdrawing the biological fluid from thedonor, separating red blood cells from the biological fluid, andreturning red blood cell-depleted platelet-containing biological fluidto the donor includes continuous flow centrifugation.
 6. The method ofclaim 1 further comprising separating gas from the flow path of theseparated red blood cells before leukocyte depleting the red bloodcells.
 7. The method of claim 6 wherein separating gas from the flowpath of the separated red blood cells includes passing the red bloodcells into a gas separation arrangement.
 8. The method of claim 7wherein passing the red blood cells into a gas separation arrangementincludes passing gas through a gas outlet and passing the red bloodcells through a drip chamber.
 9. The method of claim 8 wherein passinggas through a gas outlet includes passing gas through a porous mediumuntil red blood cells contact the porous medium and gas flow stopsautomatically.
 10. The method of claim 8 further comprising passing theleukocyte depleted red blood cells into a container.
 11. The method ofclaim 8 wherein the biological fluid comprises whole blood.
 12. Themethod of claim 8 wherein the source is a donor, the method includingwithdrawing biological fluid from the donor and returning red bloodcell-depleted platelet-containing biological fluid to the donor at leasttwice.
 13. The method of claim 1 wherein the biological fluid compriseswhole blood.